a) Field of the Invention
This invention relates to a sprag-type one-way clutch, which is adapted to be mounted between a driving shaft and a driven shaft in an automotive vehicle, general industrial equipment or the like so that motive power of rotation of the driving shaft, said rotation being only in one direction, can be transmitted to the driven shaft.
b) Description of the Related Art
A sprag-type one-way clutch is mounted between a driving shaft and a driven shaft and by way of sprags arranged between an outer ring and an inner ring, transmits rotational force of one direction from the driving shaft to the driven shaft.
When the rotational force of the one direction is applied from the driving shaft to the sprags, the sprags are wedged between the outer ring and the inner ring so that torque is transmitted to the driven shaft. Upon application of rotational force of an opposite direction, however, the sprags remain unwedged between the outer ring and the inner ring so that no transmission of torque takes place between the driving shaft and the driven shaft.
Depending primarily upon the manner of holding of sprags, these sprag-type one-way clutches can be classified into three types, that is, the single cage type, the wire cage type and the double cage type.
A description will hereinafter be made of the constructions of one-way clutches of the respective types.
A conventional one-way clutch 60 of the single cage type will be described while making reference to FIGS. 1A through 1C for the sake of convenience.
The one-way clutch 60 comprises plural sprags 13, which are to be wedged between an outer ring 21 and an inner ring 22, and a retainer 15 arranged between the outer ring 21 and the inner ring 22 and holding the sprags 13 in place.
The retainer 15 is composed of a cylindrical part 18 and a flange 17. Sprag windows 19 for the sprags 13 are formed in the cylindrical part 18. The flange 17 is formed in an elliptical or oval shape having a short-diameter portion and a long-diameter portion.
A ring-shaped spring 16 is fitted beforehand on the cylindrical part 18 of the retainer 15. When the sprags 13 are inserted in the sprag windows 19 of the cylindrical part 18 and the spring 16 is fitted in spring-receiving slots formed in the sprags 13, the sprags 13 are held in the sprag windows 19 under pressing force of the spring 16.
As has been described above, the conventional one-way clutch 60 has substantially the same construction as a one-way clutch 10 according to a first embodiment of the present invention except that the conventional one-way clutch 60 is different in the shape of the sprag windows formed in the retainer from the one-way clutch 10.
To show this difference more clearly, a side view of the conventional one-way clutch 60 of the single cage type is illustrated in FIG. 6.
If any one of the sprags 13 begins to move in an axial direction of a cylindrical part 68, one of side faces of the sprag 13, said one side face being on a side of the moving direction of the sprag 13, comes into contact with the corresponding one of two edges 692,692 out of four edges of the associated sprag window 69 formed in the retainer 65, said two edges 692,692 extending in a peripheral direction of the cylindrical part 68, so that the sprag 13 is prevented from moving in the axial direction of the cylindrical part 68.
A description will next be made of a conventional one-way clutch 70 of the wire cage type.
FIGS. 7A and 7B illustrate at numeral 70 the conventional one-way clutch of the wire cage type as assembled between an outer ring 21 and an inner ring 22. FIG. 7A is a front view of the conventional one-way clutch 70 of the wire cage type, while FIG. 7B is a vertical cross-sectional view of the same conventional one-way clutch 70 taken in the direction of arrows VIIB--VIIB of FIG. 7A.
A retainer 75 employed in this one-way clutch 70 has been formed by bending a wire in a square-U zig-zag endless form so that said wire alternately extends in an axial and peripheral directions of the retainer 75. Each sprag 13 is arranged and held in place in a sprag window which is formed of two axially-extending adjacent portions of the wire and one peripherally-extending portion of the wire, said peripherally-extending portion connecting the axially-extending portions with each other at their proximal ends.
The one-way clutch 70 is constructed by arranging the sprags 13 in the retainer 75, fitting a spring 16 in spring-receiving slots formed in the sprags 13, and the arranging two side plates 72,74 on opposite sides of the sprags 13.
Depending on which side each sprag 13 moves toward in the axial direction, one of the side faces of the sprag 13, said one side face being on a side of the moving direction of the sprag 13, comes into contact at substantially the entire area thereof with the opposing one of the side plates 72,74 (see FIG. 7B).
Finally, a conventional one-way clutch 80 of the double cage type will be described while making reference to FIGS. 4A, 4B, 5A and 5B for the sake of convenience.
The one-way clutch 80 is different in the shape of sprags and the sprag-holding structure from the above-described one-way clutch of the single cage type.
The one-way clutch 80 is constructed by holding sprags 43 in place by an outer retainer 87 shown in FIG. 8A, an inner retainer 88 depicted in FIG. 8B and a ribbon spring 50 illustrated in FIGS. 5A and 5B.
As is shown in the perspective view of FIG. 5A, the ribbon spring 50 is provided with windows formed as spaces by side bars 54, which extend in a lengthwise direction and include plural wrinkles 540 formed at equal intervals, and also by cross bars 52 extending in a widthwise direction. A wrinkle 520 extends from a central portion of each cross bar 52 and terminates in a tab 522.
FIG. 5B is a perspective view, which illustrates the sprags 43 assembled in the ribbon spring 50 shown in FIG. 5A.
When each sprag 43 with a constricted portion formed in a central part thereof is assembled in one of the windows of the ribbon spring 50, the constricted portion of the sprag 43 is brought into contact with the tab 522 of the wrinkle 520 so that the sprag 43 is urged by the wrinkle 520 via the tab 522.
The sprags 43, which are in a state assembled in the ribbon spring 50, is held by the retainers 87,88 which will be described below.
Incidentally, the outer retainer 87 is provided with resilient pieces (not shown) at several locations on an outer peripheral portion of the outer retainer 87. Resilient engagement of the resilient pieces with an inner peripheral portion of the outer ring produces drag torque.
In FIG. 4B, numerals 94,96 indicate a pair of end bearings.
FIGS. 8A and 8B are side views of the outer retainer 87 and inner retainer 88 for use in the conventional one-way clutch 80 of the double cage type.
The sprags 43 are held in sprag windows 870,880, which are formed in the outer retainer 87 and inner retainer 88, respectively.
Each of the above-described one-way clutches 60,70,80 is used by assembling it between the outer ring 21 and the inner ring 22 in such a way that the inner ring 22 is located inside the retainer or retainers and the outer ring 21 is located outside the retainer or retainers.
Each of the above-described one-way clutches of the single cage type, wire cage type and double cage type is designed so that an oil film of lubricating oil is formed at an area of contact between each edge of each sprag window of each retainer and its associated sprag or between each side plate and each sprag to produce frictional force by way of the oil film. This frictional force acts as resistance when a relative motion takes place between the retainer or retainers and the sprags or between the side plates and the sprags. It is therefore necessary to set the biasing force of the spring member at a high level in view of the resistance. As a result, excess drag torque is unavoidably produced during a slip of the clutch, leading to a problem in that the fuel economy of an automobile or a motorcycle is deteriorated.
Further, a large area of contact between each sprag and each edge of its corresponding sprag window or a large area between each sprag and each side plate tends to develop wearing at the contact area, leading to a problem in that the durability of the clutch is reduced.
The above problems tend to arise especially at low temperatures where the viscosity of the oil film becomes higher.